PISA

Protein interfaces, surfaces and assemblies service PISA at European Bioinformatics Institute http://www.ebi.ac.uk/msd-srv/prot_int/pistart.html, authored by E. Krissinel and K. Henrick. Quoting from the PISA website: "PISA is an interactive tool for the exploration of macromolecular (protein, DNA/RNA and ligand) interfaces, prediction of probable quaternary structures (assemblies), database searches of structurally similar interfaces and assemblies, as well as searches on various assembly and PDB entry parameters." PISA is a core part of CCP4.

Biological units displayed in the 'Structure Box' on Proteopedia PDB entry pages (e.g. 1h88) are predictions of the most likely biological unit as calculated by PISA, as well as all biological unit structures natively available in Proteopedia (i.e. those that were not uploaded by Proteopedia users).